Element: mousewheel event

{{APIRef}} {{deprecated_header}} {{ Non-standard_header() }} 

The obsolete and non-standard mousewheel event is fired asynchronously at an {{domxref("Element")}}  to provide updates while a mouse wheel or similar device is operated. The mousewheel event was never part of any standard, and while it was implemented by several browsers, it was never implemented by Firefox.

[!NOTE] Instead of this obsolete event, use the standard {{domxref("Element.wheel_event", "wheel")}}  event.

Syntax

Use the event name in methods like {{domxref("EventTarget.addEventListener", "addEventListener()")}} , or set an event handler property.

addEventListener("mousewheel", (event) => { })

onmousewheel = (event) => { }

Event type

A {{domxref("WheelEvent")}} . Inherits from {{domxref("MouseEvent")}} , {{domxref("UIEvent")}}  and {{domxref("Event")}} .

{{InheritanceDiagram("WheelEvent")}} 

Event properties

This interface inherits properties from its ancestors, {{DOMxRef("MouseEvent")}} , {{DOMxRef("UIEvent")}} , and {{DOMxRef("Event")}} .

• {{DOMxRef("WheelEvent.deltaX")}}  {{ReadOnlyInline}} 

  • : Returns a double representing the horizontal scroll amount.

• {{DOMxRef("WheelEvent.deltaY")}}  {{ReadOnlyInline}} 

  • : Returns a double representing the vertical scroll amount.

• {{DOMxRef("WheelEvent.deltaZ")}}  {{ReadOnlyInline}} 

  • : Returns a double representing the scroll amount for the z-axis.

• {{DOMxRef("WheelEvent.deltaMode")}}  {{ReadOnlyInline}} 

  • : Returns an unsigned long representing the unit of the delta* values’ scroll amount. Permitted values are:

    Constant	Value	Description
    WheelEvent.DOM_DELTA_PIXEL	0x00	The delta* values are specified in pixels.
    WheelEvent.DOM_DELTA_LINE	0x01	The delta* values are specified in lines. Each mouse click scrolls a line of content, where the method used to calculate line height is browser dependent.
    WheelEvent.DOM_DELTA_PAGE	0x02	The delta* values are specified in pages. Each mouse click scrolls a page of content.

• {{DOMxRef("WheelEvent.wheelDelta")}}  {{ReadOnlyInline}}  {{deprecated_inline}} 

  • : Returns an integer (32-bit) representing the distance in pixels.

• {{DOMxRef("WheelEvent.wheelDeltaX")}}  {{ReadOnlyInline}}  {{deprecated_inline}} 

  • : Returns an integer representing the horizontal scroll amount.

• {{DOMxRef("WheelEvent.wheelDeltaY")}}  {{ReadOnlyInline}}  {{deprecated_inline}} 

  • : Returns an integer representing the vertical scroll amount.

The detail property

The value of the {{domxref("UIEvent/detail", "detail")}}  property is always zero, except in Opera, which uses detail similarly to the Firefox-only {{domxref("Element.DOMMouseScroll_event", "DOMMouseScroll")}}  event’s detail value, which indicates the scroll distance in terms of lines, with negative values indicating the scrolling movement is either toward the bottom or toward the right, and positive values indicating scrolling to the top or left.

[!NOTE] On macOS, the scroll distance (and therefore the value of detail) is computed based on the accelerated scroll distance.

On Linux, 2 or -2 is set per native wheel event.

wheelDelta, wheelDeltaX and wheelDeltaY value

The wheelDelta attribute value is an abstract value which indicates how far the wheel turned. If the wheel has rotated away from the user, it’s positive, otherwise negative. This means that the delta value sign is different from DOM Level 3 Event’s wheel. However, the meaning of the amount of these values is not the same between browsers. See following explanation for the detail.

IE and Opera (Presto) only support wheelDelta attribute and do not support horizontal scroll.

The wheelDeltaX attribute value indicates the wheelDelta attribute value along the horizontal axis. When a user operates the device for scrolling to right, the value is negative. Otherwise, i.e., if it’s to left, the value is positive.

The wheelDeltaY attribute value indicates the wheelDelta attribute value along the vertical axis. The sign of the value is the same as the wheelDelta attribute value.

Chrome

On Windows, the value is the same as the delta value of WM_MOUSEWHEEL or WM_MOUSEHWHEEL. And also, the value isn’t changed even if the scroll amount of system settings is page scroll, i.e., the value is the same as IE on Windows.

On Linux, the value is 120 or -120 per native wheel event. This makes the same behavior as IE and Chrome for Windows.

On Mac, the value is complicated. The value is changed if the device that causes the native wheel event supports continuous scroll.

If the device supports continuous scroll (e.g., trackpad of MacBook or mouse wheel which can be turned smoothly), the value is computed from accelerated scroll amount. In this case, the value is the same as Safari.

If the device does not support continuous scroll (typically, old mouse wheel which cannot be turned smoothly), the value is computed from non-accelerated scroll amount (120 per notch). In this case, the value is different from Safari.

This difference makes a serious issue for web application developers. That is, web developers cannot know if mousewheel event is caused by which device.

Safari

The value is always computed from accelerated scroll amount. This is really different from other browsers except Chrome with continuous scroll supported device.

Opera (Presto)

The value is always the detail attribute value ✕ 40.

On Windows, since the detail attribute value is computed from actual scroll amount, the value is different from other browsers except the scroll amount per notch is 3 lines in system settings or a page.

On Linux, the value is 80 or -80 per native wheel event. This is different from other browsers.

On Mac, the detail attribute value is computed from accelerated scroll amount of native event. The value is usually much bigger than Safari’s or Chrome’s value.

Specifications

Not part of any specification.

Browser compatibility

{{Compat}} 

See also

• The standard {{domxref("Element/wheel_event", "wheel")}}  event to listen to instead.